Do you remember that Suzanne Vega song that went: "My name is Luca. I live on the second floor. I live upstairs from you. Yes, I think you've seen me before." Yeah, he's not the Luca in question. Instead, I'm talking about our last universal common ancestor or LUCA. While some people think we can trace our human origins back to one common female ancestor from Africa, LUCA rides on the idea that all life, not just human life, derives from a single microorganism. We're talking plants, animals, bacteria, fungus -- the whole biological spectrum that encompasses life today.

Think about that for a second. It's pretty amazing. Estimates for the number of species on Earth vary wildly, but let's take birds, for example. According to Britannica, there are about 9,600 species around today. Now throw in reptiles, amphibians, insects and strange things like moss animals -- these tiny matlike filter feeders that look like their namesake -- and you start to realize how crazy it is that all these diverse organisms may have evolved from a single ancestor.

That has to be one special organism, and indeed, the 3.8-billion-year-old ancestor certainly was, according to a paper published by researchers from the University of Montreal and the University of Lyon. But one thing our LUCA wasn't: an extremophile. Scientists expected LUCA to resemble one of those daredevil organisms that makes its home near hot springs or along oceanic vents, but no. LUCA was more stable than they gave it credit for. And the tiny creature was sensitive to the heat, too, preferring to reside in cooler temperatures. That preference for temperature might seem arbitrary, but it actually helps scientists to advance the theory of an early RNA world, rather than a DNA one.